A number of recombinant cytokines are used in a variety of clinical settings. These include interleukin-2 (IL-2), GM-CSF, IL-11, IL-12 and type I interferons (IFNs). These proteins are primarily being used as stimulators of immune cells and to act as growth factors or to enhance anti-cancer or viral responses. Few cytokines have been used to inhibit the immune system; for example, inhibition has been attempted with IL-10, which works indirectly on accessory cell functions necessary for T cell functions and which was being developed specifically with Crohn's disease and Inflammatory Bowel Disease as targets, and TGF. Success with these has been limited.
Antagonists of IL-12 p40 have been tested in clinical trials for patients with Crohn's disease with some success.
Antagonists of IL-15 are in clinical trials for arthritis based on the observation that this cytokine was involved in the development of this disease.
The IL-1 receptor antagonist is a commercially available product that is used to treat patients with rheumatoid arthritis. This is a product that blocks the interaction of the pro-inflammatory cytokine IL-1 with its receptor.
Several companies have developed antibodies/antagonists specific for the cytokine TNF-α which are currently used in the treatment of patients with rheumatoid arthritis. This approach relies on the neutralization of endogenous cytokine to prevent inflammation. A similar approach has been pursued with antibodies specific for IL-1 and IL-6. One safety issue is that these treatments are associated with the development of opportunistic infections including TB and toxoplasmosis.